It is necessary to make periodic inspections of the interior of pipe and conduits carrying hazardous fluids and other fluids leakage of which cannot be tolerated. Pipes and conduits of appropriate size have been inspected by various types of devices which travel or are propelled through the pipes, carrying cameras or other inspection devices. It is not unduly difficult to design such a vehicle for a truly circular pipe of fixed diameter as it can propel itself by traction along geometrically opposite areas of the pipe wall. However, ideal conditions are seldom found in pipe lines and conduits, particularly at bends. Furthermore prior art vehicles have difficulty maintaining traction on inclined surfaces against the pull of gravity.